1. Field of Invention
This invention relates in general to catalytic converter assemblies, and more specifically, to a method of selectively matching the catalytic substrate's size to a support material's weight factor.
2. Background of Related Art
Catalytic converters include a catalytic element housed in a metallic housing. The housing typically includes a conical-shaped first end and a conical-shaped second end. The catalytic converters are typically manufactured by cutting a metallic tubular member to a desired length. The catalytic element is pre-wrapped by a support material (i.e., mat) and inserted within the housing. The tubular member is then deformed radially inward so as to compress the outer diameter of the housing to a final preset outside profile dimension.
The support material is compressed between the housing and the catalytic substrate. A typical tolerance of a substrate's outer profile dimension is +/−1 mm. This allows the dimensional variation of a substrate's outer profile dimension to be between 0-2 mm. Meanwhile, there is a +/−10% variation in the support material's weight. Utilizing a known deforming process, for example a swaging process, the housing is deformed only to a preset outside profile dimension which avoids over compression of the housing so as to not fracture the catalytic substrate secured therein.
Since the deforming process deforms the housing only to a preset outside profile, inherent variations of the catalytic elements can affect the performance of the catalytic converter. For example, if the dimensional stack-up of the substrate and the support material is very high prior to assembly, the catalytic substrate may fracture or if the dimensional stack-up is small, then the substrate may move within housing during vehicle operation. In each example, the end result may produce emissions failure.
Methods and apparatus for manufacturing a catalytic converter such as that disclosed in U.S. Pat. No. 6,954,988 determine the fracture characteristics of the substrate and the mat material. The mat and substrate are inserted into the housing as a pre-assembly. The housing (including the mat and substrate) is compressed according to a compression sequence (compression of the housing and mat over the substrate at a respective distance over a respective time) to avoid fracture of the substrate. Due to part to part variation of the components, if a catalytic converter housing requires more than one set of substrates and mat materials, then more than one compression sequence may be required to assure similar compression for each of the sub-assemblies. If such compensation is not made, the first compression sequence is most likely not suitable for securing the second pre-assembly and vice-versa. Utilizing one of the respective compression sequences for both pre-assemblies could result in one or both substrates being loose or fractured.